The present invention relates to a method of maintaining a low bacterial content in a compressor that includes a coolant circulating system, wherewith operating gas and coolant are supplied to the compressor during running of the system and the gas is compressed to an outlet pressure, the gas and the coolant are removed together from the compressor and then separated into a gas and a liquid phase, whereafter the gas is passed to a recipient and the liquid is cooled before being returned to the compressor as coolant. The invention also relates to a compressor with an associated coolant circulating system, for maintaining a low bacteria content in the compressor.
Compressors intended for compressing air or some other gas that is then delivered to a recipient, such as a pressure gas system for example, are often cooled with a liquid coolant, e.g. water. This coolant comes into direct contact with the gas under compression. Normally at least some of the coolant is vaporised by the heat generated during compression. As a result, it is then necessary to subject the compressed coolant-containing gas to a gas-liquid separation process in order to recover the coolant. Moreover, it is also often desired that the gas will contain very little coolant, in other words that the amount of coolant present in the gas passed to the recipient is the least possible.
Typical coolants are oil and water. It is very much desired to establish in the coolant circulation system conditions in which bacteria are unable to flourish, particularly when the coolant is water and the gas is air. Bacterial growth will normally occur in particular in those parts of the circulation system in which the liquid has a low rate of flow or is stationary. The temperature prevailing in these parts of the system is also normally favourable to the growth of bacteria. Thus, there is obtained rapidly growing colonies of bacteria that form a slimy mass. Bacterial growth is normally exponential.
In order to ensure that the compressed gas (usually air) will not contain large quantities of bacteria subsequent to the liquid separation stage, it is therefore necessary to dispose of the bacteria colonies intermittently, before the colonies become too large. This removal can be achieved either by removing all the liquid present and replacing it with clean liquid or by continuously cleansing the liquid circulating in the system. Even when the coolant is water, it is still expensive to cleanse at least parts of the water circulating system and adding in the order of 40 litres of distilled or de-ionised water at relatively short intervals.
One object of the present invention is to provide a simple and effective method by means of which the growth of harmful bacteria in the coolant circuit of a compressor can be prevented.
Another object is to provide a compressor with a coolant system that is able to prevent or greatly reduce the growth of bacteria in the coolant circuit.
According to the present invention the ability of the compressor to generate heat is appropriated to raise the temperature of the coolant to a bacteria-killing level for a period of time sufficient to pasteurise the coolant. Delivery of the compressed gas to a recipient, e.g. the pressure gas system, is avoided during this time period and the gas is either passed to the surroundings or preferably returned to the gas inlet of the compressor. In this latter alternative, a large portion of the coolant that would otherwise have been lost is returned to the system. In order to attain the conditions which cause the temperature of the coolant to increase, it is necessary to reduce the extent to which the coolant is cooled in operation. Cooling of the coolant is ceased completely during this bacteria-killing process, so as to obtain the quickest possible increase in temperature to the level desired.
The temperature of the coolant is controlled with the aid of a temperature sensor disposed between the coolant cooling device, or heat exchanger, and the coolant inlet of the compressor or in the inlet itself.
Pasteurisation of the coolant can be initiated either automatically or manually. The actual pasteurisation process and the duration of said process can be controlled with the aid of appropriate control devices, such as with the aid of valves for example.
The former object is achieved in accordance with the invention with a method for maintaining a low bacteria content in a compressor that includes a coolant circulation system, wherein gas and coolant are delivered to the compressor during operation and the gas is compressed to an outlet pressure, wherein gas and coolant are removed together from the compressor and the gas and coolant then separated into a respective gas phase and a liquid phase, whereafter the gas phase is passed to a recipient and the liquid phase is cooled before being returned to the compressor as a coolant. The method is characterised by creating bacteria-killing conditions intermittently in the system, by virtue of utilising the heat-generating capacity of the compressor to raise the temperature of the circulating coolant to a temperature of at least 55xc2x0 C. for a duration of at least 15 seconds.
Advantageous embodiments will be apparent from the accompanying dependent claims.
The latter object is achieved with a compressor that has an associated coolant circulation system and that includes a gas inlet, a coolant inlet separate from the gas inlet, and a common outlet for compressed-gas and coolant, and wherein the circulation system includes a separator which includes a gas/coolant inlet means, a gas phase outlet means, a liquid phase outlet means, a heat exchanger for lowering the temperature of the liquid phase, and conduits that connect the compressor outlet with the separator inlet, the liquid phase outlet of the separator with the heat exchanger, and the heat exchanger with the coolant inlet of the compressor. The inventive compressor is characterised in that it includes a temperature sensor in the coolant inlet of the compressor or in the coolant conduit that connects the heat exchanger with the coolant inlet of said compressor.